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Title: Productions of I, I{sup *}, and C{sub 2}H{sub 5} in the A-band photodissociation of ethyl iodide in the wavelength range from 245 to 283 nm by using ion-imaging detection

Abstract

Photodissociation dynamics of ethyl iodide in the A band has been investigated at several wavelengths between 245 and 283 nm using resonance-enhanced multiphoton ionization technique combined with velocity map ion-imaging detection. The ion images of I, I{sup *}, and C{sub 2}H{sub 5} fragments are analyzed to yield corresponding speed and angular distributions. Two photodissociation channels are found: I(5p {sup 2}P{sub 3/2})+C{sub 2}H{sub 5} (hotter internal states) and I{sup *}(5p {sup 2}P{sub 1/2})+C{sub 2}H{sub 5} (colder). In addition, a competitive ionization dissociation channel, C{sub 2}H{sub 5}I{sup +}+h{nu}{yields}C{sub 2}H{sub 5}+I{sup +}, appears at the wavelengths <266 nm. The I/I{sup *} branching of the dissociation channels may be obtained directly from the C{sub 2}H{sub 5}{sup +} images, yielding the quantum yield of I{sup *} about 0.63-0.76, comparable to the case of CH{sub 3}I. Anisotropy parameters ({beta}) determined for the I{sup *} channel remain at 1.9{+-}0.1 over the wavelength range studied, indicating that the I{sup *} production should originate from the {sup 3}Q{sub 0} state. In contrast, the {beta}(I) values become smaller above 266 nm, comprising two components, direct excitation of {sup 3}Q{sub 1} and nonadiabatic transition between the {sup 3}Q{sub 0} and {sup 1}Q{sub 1} states. The curve crossing probabilities are determined tomore » be 0.24-0.36, increasing with the wavelength. A heavier branched ethyl group does not significantly enhance the I(5p {sup 2}P{sub 3/2}) production from the nonadiabatic contribution, as compared to the case of CH{sub 3}I.« less

Authors:
; ; ; ;  [1];  [2];  [2];  [2];  [2];  [2];  [2];  [2]
  1. State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan, Beijing 430071 (China)
  2. (China)
Publication Date:
OSTI Identifier:
20991219
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 126; Journal Issue: 6; Other Information: DOI: 10.1063/1.2435341; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; BRANCHING RATIO; DISSOCIATION; IODIDES; IODINE IONS; METHYL IODIDE; MULTI-PHOTON PROCESSES; PHOTOIONIZATION; PHOTOLYSIS; REACTION KINETICS

Citation Formats

Tang, Ying, Lee, Wei-Bin, Hu, Zhengfa, Zhang, Bing, Lin, King-Chuen, Graduate School of Chinese Academy of Sciences, Wuhan, Beijing 437001, Department of Chemistry, National Taiwan University, Taipei 106, Taiwan, Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan, Beijing 430071, Graduate School of Chinese Academy of Sciences, Wuhan, Beijing 437001, Department of Chemistry, National Taiwan University, Taipei 106, Taiwan, and Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan. Productions of I, I{sup *}, and C{sub 2}H{sub 5} in the A-band photodissociation of ethyl iodide in the wavelength range from 245 to 283 nm by using ion-imaging detection. United States: N. p., 2007. Web. doi:10.1063/1.2435341.
Tang, Ying, Lee, Wei-Bin, Hu, Zhengfa, Zhang, Bing, Lin, King-Chuen, Graduate School of Chinese Academy of Sciences, Wuhan, Beijing 437001, Department of Chemistry, National Taiwan University, Taipei 106, Taiwan, Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan, Beijing 430071, Graduate School of Chinese Academy of Sciences, Wuhan, Beijing 437001, Department of Chemistry, National Taiwan University, Taipei 106, Taiwan, & Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan. Productions of I, I{sup *}, and C{sub 2}H{sub 5} in the A-band photodissociation of ethyl iodide in the wavelength range from 245 to 283 nm by using ion-imaging detection. United States. doi:10.1063/1.2435341.
Tang, Ying, Lee, Wei-Bin, Hu, Zhengfa, Zhang, Bing, Lin, King-Chuen, Graduate School of Chinese Academy of Sciences, Wuhan, Beijing 437001, Department of Chemistry, National Taiwan University, Taipei 106, Taiwan, Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan, Beijing 430071, Graduate School of Chinese Academy of Sciences, Wuhan, Beijing 437001, Department of Chemistry, National Taiwan University, Taipei 106, Taiwan, and Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan. Wed . "Productions of I, I{sup *}, and C{sub 2}H{sub 5} in the A-band photodissociation of ethyl iodide in the wavelength range from 245 to 283 nm by using ion-imaging detection". United States. doi:10.1063/1.2435341.
@article{osti_20991219,
title = {Productions of I, I{sup *}, and C{sub 2}H{sub 5} in the A-band photodissociation of ethyl iodide in the wavelength range from 245 to 283 nm by using ion-imaging detection},
author = {Tang, Ying and Lee, Wei-Bin and Hu, Zhengfa and Zhang, Bing and Lin, King-Chuen and Graduate School of Chinese Academy of Sciences, Wuhan, Beijing 437001 and Department of Chemistry, National Taiwan University, Taipei 106, Taiwan and Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan and State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan, Beijing 430071 and Graduate School of Chinese Academy of Sciences, Wuhan, Beijing 437001 and Department of Chemistry, National Taiwan University, Taipei 106, Taiwan and Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan},
abstractNote = {Photodissociation dynamics of ethyl iodide in the A band has been investigated at several wavelengths between 245 and 283 nm using resonance-enhanced multiphoton ionization technique combined with velocity map ion-imaging detection. The ion images of I, I{sup *}, and C{sub 2}H{sub 5} fragments are analyzed to yield corresponding speed and angular distributions. Two photodissociation channels are found: I(5p {sup 2}P{sub 3/2})+C{sub 2}H{sub 5} (hotter internal states) and I{sup *}(5p {sup 2}P{sub 1/2})+C{sub 2}H{sub 5} (colder). In addition, a competitive ionization dissociation channel, C{sub 2}H{sub 5}I{sup +}+h{nu}{yields}C{sub 2}H{sub 5}+I{sup +}, appears at the wavelengths <266 nm. The I/I{sup *} branching of the dissociation channels may be obtained directly from the C{sub 2}H{sub 5}{sup +} images, yielding the quantum yield of I{sup *} about 0.63-0.76, comparable to the case of CH{sub 3}I. Anisotropy parameters ({beta}) determined for the I{sup *} channel remain at 1.9{+-}0.1 over the wavelength range studied, indicating that the I{sup *} production should originate from the {sup 3}Q{sub 0} state. In contrast, the {beta}(I) values become smaller above 266 nm, comprising two components, direct excitation of {sup 3}Q{sub 1} and nonadiabatic transition between the {sup 3}Q{sub 0} and {sup 1}Q{sub 1} states. The curve crossing probabilities are determined to be 0.24-0.36, increasing with the wavelength. A heavier branched ethyl group does not significantly enhance the I(5p {sup 2}P{sub 3/2}) production from the nonadiabatic contribution, as compared to the case of CH{sub 3}I.},
doi = {10.1063/1.2435341},
journal = {Journal of Chemical Physics},
number = 6,
volume = 126,
place = {United States},
year = {Wed Feb 14 00:00:00 EST 2007},
month = {Wed Feb 14 00:00:00 EST 2007}
}
  • The speed and angular distribution of O atoms arising from the photofragmentation of C{sub 5}H{sub 8}-O{sub 2}, the isoprene-oxygen van der Waals complex, in the wavelength region of 213-277 nm has been studied with the use of a two-color dissociation-probe method and the velocity map imaging technique. Dramatic enhancement in the O atoms photo-generation cross section in comparison with the photodissociation of individual O{sub 2} molecules has been observed. Velocity map images of these 'enhanced' O atoms consisted of five channels, different in their kinetic energy, angular distribution, and wavelength dependence. Three channels are deduced to be due to themore » one-quantum excitation of the C{sub 5}H{sub 8}-O{sub 2} complex into the perturbed Herzberg III state ({sup 3}{Delta}{sub u}) of O{sub 2}. This excitation results in the prompt dissociation of the complex giving rise to products C{sub 5}H{sub 8}+O+O when the energy of exciting quantum is higher than the complex photodissociation threshold, which is found to be 41740 {+-} 200 cm{sup -1} (239.6{+-}1.2 nm). This last threshold corresponds to the photodissociation giving rise to an unexcited isoprene molecule. The second channel, with threshold shifted to the blue by 1480 {+-} 280 cm{sup -1}, corresponds to dissociation with formation of rovibrationally excited isoprene. A third channel was observed at wavelengths up to 243 nm with excitation below the upper photodissociation threshold. This channel is attributed to dissociation with the formation of a bound O atom C{sub 5}H{sub 8}-O{sub 2}+hv{yields} C{sub 5}H{sub 8}-O{sub 2}({sup 3}{Delta}{sub u}) {yields} C{sub 5}H{sub 8}O + O and/or to dissociation of O{sub 2} with borrowing of the lacking energy from incompletely cooled complex internal degrees of freedom C{sub 5}H{sub 8}{sup *}-O{sub 2}+hv{yields} C{sub 5}H{sub 8}{sup *}-O{sub 2}({sup 3}{Delta}{sub u}) {yields} C{sub 5}H{sub 8}+ O + O. The kinetic energy of the O atoms arising in two other observed channels corresponds to O atoms produced by photodissociation of molecular oxygen in the excited a {sup 1}{Delta}{sub g} and b {sup 1}{Sigma}{sub g}{sup +} singlet states as the precursors. This indicates the formation of singlet oxygen O{sub 2}(a {sup 1}{Delta}{sub g}) and O{sub 2}(b {sup 1}{Sigma}{sub g}{sup +}) after excitation of the C{sub 5}H{sub 8}-O{sub 2} complex. Cooperative excitation of the complex with a simultaneous change of the spin of both partners {sup 1}X-{sup 3}O{sub 2}+h{nu}{yields}{sup 3}X-{sup 1}O{sub 2}{yields}{sup 3}X +{sup 1}O{sub 2} is suggested as a source of singlet oxygen O{sub 2}(a {sup 1}{Delta}{sub g}) and O{sub 2}(b {sup 1}{Sigma}{sub g}{sup +}). This cooperative excitation is in agreement with little or no vibrational excitation of O{sub 2}(a {sup 1}{Delta}{sub g}), produced from the C{sub 5}H{sub 8}-O{sub 2} complex as studied in the current paper as well as from the C{sub 3}H{sub 6}-O{sub 2} and CH{sub 3}I-O{sub 2} complexes reported in our previous paper [Baklanov et al., J. Chem. Phys. 126, 124316 (2007)]. The formation of O{sub 2}(a {sup 1}{Delta}{sub g}) from C{sub 5}H{sub 8}-O{sub 2} was observed at {lambda}{sub pump}= 213-277 nm with the yield going down towards the long wavelength edge of this interval. This spectral profile is interpreted as the red-side wing of the band of a cooperative transition {sup 1}X-{sup 3}O{sub 2}+h{nu}{yields}{sup 3}X(T{sub 2})-{sup 1}O{sub 2}(a {sup 1}{Delta}{sub g}) in the C{sub 5}H{sub 8}-O{sub 2} complex.« less
  • The results of a study of the dynamics of photodissociation of the (NO)/sub 2//sup +//sup ./ cluster ion to form NO/sup +/+NO/sup ./ in the 488--660 nm range are presented. The experiments were performed by crossing a high energy ion beam with a laser beam. Product kinetic energy distributions were derived from the experimental measurements along with information about the angular distribution of the products. Except at the lowest photon energy at which experiments were performed (where the product relative velocity is comparable to the rotational velocity of (NO)/sub 2//sup +//sup ./), the product angular distributions could be adequately fitmore » by an angular distribution of the form 1+..beta..P/sub 2/(theta) with a value for ..beta.. of 1.3. The product kinetic energy distributions are characteristic of dissociation occurring on a repulsive surface. The fraction of the available energy partitioned into relative kinetic energy increases from 22% at 659 nm to 32% at 488 nm. The data on the product angular distributions indicate that photodissociation occurs by a transition to an excited state with a lifetime that is negligible compared with a rotational period, and that the polarization of the transition is predominantly along the NO--NO/sup +/ axis in the cluster. The fraction of available energy partitioned into relative kinetic energy can be accounted for by using a simple impulsive model plus vibrational excitation due to changes in equilibrium geometries of the NO/sup ./ and NO/sup +/ moieties.« less
  • High precision measurements of the vapor pressure differences between some deuterated benzenes B-d/sub x/ (x=1, para-2, and 6) and protio benzene B-d/sub 0/; between para- and ortho-, and para- and meta-dideuterobenzene; and between perdeuterocyclohexane C-d/sub 12/ and protiocyclohexane C-d/sub 0/ were made from near the freezing point to the normal boiling point. The data are best represented as the logarithmic ratios ln R (d/sub 6/) =ln (P/sub d/0/P/sub d/6) =1226.5/T/sup 2/-12.178/T, ln R (para/ortho) =ln (P/sub parahyphend/2/P/sub orthohyphend/2) =2.6/T/sup 2/, and ln R (para/meta) =ln (P/sub parahyphend/2/P/sub metahyphend/2) =-2.0/T/sup 2/, together with the deviations from the law of the meanmore » ..delta.. (d1) =6-(ln R (d/sub 6/)/lnR (d/sub 1/))=0.177-3.6 x 10/sup -4/t and ..delta.. (d/sub 2hyphenpara/=3-(ln R (d/sub 6/)/ln R (d/sub 2hyphenpara/))=0.028 +1.0 x 10/sup -4/t. The isotope effects are inverse and display significant deviations from the law of the mean. The cyclohexane results are given by ln R (C-d/sub 12/) =-2188.4/T/sup 2/-18.587/T. New measurements of the vapor pressures of benzene--cyclohexane solutions are also reported between 5 and 80 /sup 0/C. The data are in good agreement with the best earlier work. Excess free energies of the equimolar solutions B-h/sub 6//B-d/sub 6/ and C-h/sub 12//C-d/sub 12/ have been measured between 20 and 80 /sup 0/C. Suitable fits to the data yield the following results (30 /sup 0/C); G/sup ex/(B-h/B-d), G/sup ex/(C-h/C-d); H/sup ex/(B-h/B-d),« less
  • The photodissociation dynamics of the ethyl radical C{sub 2}H{sub 5} has been investigated by velocity map imaging. Ethyl was produced by flash pyrolysis from n-propyl nitrite and excited to the A {sup 2}A{sup Prime} (3s) Rydberg state around 250 nm. The energetically most favorable reaction channel in this wavelength region is dissociation to C{sub 2}H{sub 4} (ethene) + H. The H-atom dissociation products were ionized in a [1+1{sup Prime }] process via the 1s-2p transition. The observed translational energy distribution is bimodal: A contribution of slow H-atoms with an isotropic angular distribution peaks at low translational energies. An expectation valuemore » for the fraction of excess energy released into translation of = 0.19 is derived from the data, typical for statistical dissociation reactions. In addition, a fast H-atom channel is observed, peaking around 1.8 eV. The latter shows an anisotropic distribution with {beta}= 0.45. It originates from a direct dissociation process within less than a rotational period. Time-delay scans with varying extraction voltages indicate the presence of two rates for the formation of H-atoms. One rate with a sub-nanosecond time constant is associated with H-atoms with large translational energy; a second one with a time constant on the order of 100 ns is associated with H-atoms formed with low translational energy. The data confirm and extend those from previous experiments and remove some inconsistencies. Possible mechanisms for the dissociation are discussed in light of the new results as well as previous ones.« less
  • Reactions between Ru(C{sub 2}Me)(PPh{sub 3}){sub 2}({eta}-C{sub 5}H{sub 5}) or Ru(C{sub 2}Ph)(L){sub 2}({eta}-C{sub 5}H{sub 5}) (L{sub 2} = (PPh{sub 3}){sub 2}, dppe, (CO)(PPh{sub 3})) and (CF{sub 3}){sub 2}C=C(CN){sub 2} gave the corresponding {sigma}-cyclobutenyl complexes, of which Ru(C=CPhC(CF{sub 3}){sub 2}C(CN){sub 2})(CO)(PPh{sub 3})({eta}-C{sub 5}H{sub 5}) (1g) was fully characterized by X-ray crystallography. Thermal isomerization of the dppe and (CO)(PPh{sub 3}) complexes to the {sigma}-buta-1,3-dien-2-yl derivatives occurred; under CO, two isomers of Ru(C(=C(CN){sub 2})CMe=C(CF{sub 3}){sub 2})(CO)(PPh{sub 3})({eta}-C{sub 5}H{sub 5}) were formed. The X-ray structures of one of these (2h), and the phenyl analogue (2g), were determined. The allyls Ru({eta}{sup 3}-C(CF{sub 3}){sub 2}CXC=C(CN){sub 2})(PPh{sub 3})({eta}-C{submore » 5}H{sub 5}) (X = Me (3d), Ph (3g)) were obtained thermally or photochemically; the structure of 3g was also determined, thus completing the series {sigma}-cyclobutenyl, {sigma}-butadienyl, {eta}{sup 3}-allyl derived from the same metal/ligand combinations. Crystal data for 1g: orthorhombic, space group P2{sub 1}2{sub 1}2{sub 1}, a = 10.409 (2) {angstrom}, b = 16.227 (3) {angstrom}, c = 20.000 (3) {angstrom}, Z = 4; 2,851 data were refined to R = 0.040, R{sub w} = 0.041. Crystal data for 2g; monoclinic, space group P2{sub 1}/n, a = 14.942 (1) {angstrom}, b = 13.413 (2) {angstrom}, c = 16.928 (6) {angstrom}, {beta} = 97.02 (1){degree}, Z = 4; 3,659 data were refined to R = 0.045, R{sub w} = 0.059. Crystal data for 2h: monoclinic, space group C2/c, a = 22.237 (4) {angstrom}, b = 18.648 (5) {angstrom}, c = 17.731 (3) {angstrom}, {beta} = 124.93 (2){degree}, Z = 8; 3,076 data were refined to R = 0.039, R{sub w} = 0.042.« less